1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device.
2. Related Art
A manufacturing process of a semiconductor device includes a step of shaping a mask material in a desired pattern (to be also referred to as patterning hereinafter). In this step, a mask material is patterned by using a photolithography technique and etching. As ordinary etching for a mask material, an RIE (Reactive Ion Etching) method as an anisotropic etching is used.
However, depending on the density of a pattern, a reaction product obtained by etching adheres to a base portion of a patterned mask material. For example, when a silicon nitride film is anisotropically etched as a mask material to pattern a gate electrode, a quantity of the reaction product adheres to a lower side-wall portion of the silicon nitride film in a region in which the pattern density of the gate electrode is low. For this reason, the width of the gate electrode disadvantageously changes depending on the density of the pattern. This causes variations in characteristic of semiconductor devices.